1. Field of the Invention
The present invention relates generally to a semiconductor laser device used for reproducing information from optical disks with different formats, such as a compact disk (CD) and a digital video disk (DVD), in a single optical pickup device.
2. Related Background Art
Currently, the CD market is the largest market among the optical disk markets. In the device for reproducing information from CDs, a near infrared semiconductor laser element with a wavelength in a 780 nm to 800 nm band has been used. On the other hand, for recording and reproduction with respect to DVDs, which are optical media with higher recording density and are expected to come into wide use rapidly in the future, a red-color semiconductor laser element with a shorter wavelength in a 635 nm to 680 nm band has been used, since a light spot is required to have a small diameter. It has been requested to enable information to be recorded and reproduced with respect to two such kinds of optical disks with different standards in one device. An optical pickup device for such a purpose is described, for example, in JP 10(1998)-320815. FIG. 9 shows a configuration of a conventional optical pickup device.
An operational principle of the conventional optical pickup device is described with reference to FIG. 9 as follows.
For recording and reproduction with respect to a CD, a semiconductor laser element 101 with a wavelength of 780 nm is used. A beam 116 emitted from the semiconductor laser element 101 in the direction perpendicular to the surface of an optical disk 106 is diverged into three beams by a diffraction grating 115. A collimator lens 103 disposed on an optical axis converts the divergent beam into a parallel beam. The parallel beam goes through a wavelength deflection filter 109 and is focused on the optical disk 106 by an objective lens 105.
The beam reflected by the optical disk 106 is converted from a divergent beam into a parallel beam by the objective lens 105 and goes through the wavelength deflection filter 109 again. Subsequently, the beam is converted into a converged beam by the collimator lens 103 and then enters a hologram element 111. The beams divided by the hologram element 111 are detected as electric signals in receiving optics 113. Based on the detected signals, the reproduction and focusing/tracking servo are carried out with respect to the CD.
On the other hand, for recording and reproduction with respect to a DVD, a semiconductor laser element 102 with a wavelength of 635 nm (or 650 nm) is used. A beam 117 emitted from the semiconductor laser element 102 in a direction parallel to the surface of an optical disk 106 is converted from a divergent beam into a parallel beam by a collimator lens 104 disposed on an optical axis and goes through a polarization beam splitter 107 and a xc2xc wavelength plate 108. Subsequently, the beam is reflected by the wavelength deflection filter 109 so that its path is deflected by 90xc2x0, and then is focused on the optical disk 106 by the objective lens 105.
The beam reflected by the optical disk 106 is converted from a divergent beam into a parallel beam by the objective lens 105 and is reflected by the wavelength deflection filter 109 again so that its path is deflected by 90xc2x0. Subsequently, its polarization direction is changed by the xc2xc wavelength plate 108. Therefore, the beam entering the polarization beam splitter 107 is reflected so that its path is deflected by 90xc2x0, and then is converged by a detection lens 110. The converged beam goes through a cylindrical lens 112 and is detected as an electric signal in receiving optics 114. Based on this detection signal, reproduction and focusing/tracking servo are carried out with respect to the DVD.
In the above-mentioned configuration, the semiconductor laser with a wavelength of 780 nm is mounted and therefore recording and reproduction also can be carried out with respect to CD-Rs.
However, such a conventional optical pickup device as shown in FIG. 9 is configured with many optical components such as two semiconductor laser elements 101 and 102 with different emission wavelengths and a plurality of receiving optics 113 and 114 for respective beams emitted from the semiconductor laser elements 101 and 102, as well as the hologram element 111, the cylindrical lens 112, the wavelength deflection filter 109, and the like. Therefore, it is difficult to reduce the size of the device.
Moreover, since the respective optical components are disposed discretely, a lot of positional adjustments and fixation are required, and thus great amounts of time and cost are required for the assembly, which have been problems.
Therefore, the present invention was made to solve the aforementioned conventional problems. The present invention is intended to provide a small and inexpensive semiconductor laser device capable of carrying out recording and reproduction with respect to various optical disks with different formats and to provide an optical pickup device having the same.
In order to achieve the above-mentioned object, a semiconductor laser device according to the present invention includes a receiving/emitting optics integrated substrate and an optical element. In the receiving/emitting optics integrated substrate, a first semiconductor laser element, a second semiconductor laser element, and a plurality of receiving optics are integrated on a substrate. The first and second semiconductor laser elements have different emission wavelengths. A distance L1, when measured in air, from the first semiconductor laser element to a focusing member is substantially equal to a distance L2, when measured in air, from the second semiconductor laser element to the focusing member.
According to this configuration, the two semiconductor laser elements and the plurality of receiving optics are integrated in the receiving/emitting optics integrated substrate, so that a small and inexpensive semiconductor laser device can be provided. In addition, since the distances, when measured in air, from the two semiconductor laser elements to the focusing member are substantially equal, one single focusing member (for instance, a collimator lens) can be employed. Thus, the optical configuration is simplified.
In the semiconductor laser device according to the present invention, preferably, a difference between the distance L1 and the distance L2, when measured in air, is within xc2x150 xcexcm.
According to this configuration, particularly the influence of aberration can be suppressed to a low level and it becomes easy to configure the optical pickup device employing a single focusing member.
In the semiconductor laser device according to the present invention, preferably, the optical element is disposed in an optical path at least between the first or second semiconductor laser element and the focusing member.
This configuration enables return light from the optical disk to diverge efficiently to be lead to the receiving optics.
In addition, it is preferable that the optical element includes a member allowing a distance for which a beam emitted from the first semiconductor laser element travels to go through the optical element to be different from a distance for which a beam emitted from the second semiconductor laser element travels to go through the optical element.
According to this configuration, the distances for which the two emitted beams travel to go through the optical element are made different, so that the distances, when measured in air, for which the two emitted beams travel after leaving the optical element can be made substantially the same.
It also is preferable that a light diverging member is formed in the optical element and a diffraction grating, a reflector, or the like is used as the light diverging member.
In the semiconductor laser device according to the present invention, preferably, the first semiconductor laser element has an emission wavelength in a 780 nm band, and the second semiconductor laser element has an emission wavelength in a 650 nm band.
According to this configuration, recording and reproduction can be carried out with respect to optical disks with both the CD format and the DVD format.
Preferably, the light diverging member exhibits different diverging efficiencies depending on wavelengths.
According to this configuration, for example, when a diffraction grating is used as the light diverging member, a semiconductor laser device can be obtained which has light diverging efficiencies optimized with respect to respective wave lengths through adjustment of the depth of the diffraction grating. When using this, therefore, an optical pickup device with excellent light utilization efficiency can be configured. Consequently, a low power consumption type optical pickup device can be obtained.
Furthermore, in the semiconductor laser device according to the present invention, it is preferable that the substrate is a silicon substrate with a principal plane that is a plane obtained when a plane equivalent to a plane (100) is rotated about an axis extending in a direction equivalent to a direction  less than 0-11 greater than  by 5xc2x0 to 15xc2x0 in a direction equivalent to a direction  less than 100 greater than , concave portions are formed in the substrate, the first and second semiconductor laser elements are placed on bottom surfaces of the concave portions, and each beam emitted from the first and second semiconductor laser elements is reflected by one side face of the corresponding concave portion.
According to this configuration, when the concave portions are formed at the surface of the silicon substrate by anisotropic etching using a potassium hydroxide-based etchant, a plane equivalent to a plane (111) can be formed as one of side faces of each concave portion, having an angle of 40xc2x0 to 50xc2x0 with respect to the bottom surface of the concave portion. Therefore, when the first and second semiconductor laser elements are disposed on the bottom surfaces of the concave portions, the one of side faces of each concave portions serves as a reflecting mirror and thus emitted beams can be lead out upward in the direction substantially perpendicular to the silicon substrate. Furthermore, the plurality of receiving optics are formed in the area where the concave portions are not formed, so that the receiving/emitting optics integrated substrate can be configured easily.
In the semiconductor laser device according to the present invention, it is preferable that the receiving/emitting optics integrated substrate and the optical element are disposed in one case.
According to this configuration, a plurality of elements can be disposed in one case and the whole is sealed, so that the reliability can be improved easily. In addition, when this case is formed as one optical unit, its handling in the assembly of an optical pickup device is considerably easier as compared to the case where separate elements are handled. Thus, the assembly process and line can be simplified.
In order to achieve the above-mentioned object, an optical pickup device according to the present invention includes a focusing member and a semiconductor laser device provided with a receiving/emitting optics integrated substrate disposed in a case, and an optical element. In the receiving/emitting optics integrated substrate, a first semiconductor laser element, a second semiconductor laser element, and a plurality of receiving optics are integrated on a substrate. The first and second semiconductor laser elements have different emission wavelengths. The optical element is disposed in the same case as that including the receiving/emitting optics integrated substrate. A distance L1, when measured in air, from the first semiconductor laser element to the focusing member is substantially equal to a distance L2, when measured in air, from the second semiconductor laser element to the focusing member. The focusing member is positioned to be fixed to the case of the semiconductor laser device.
According to this configuration, the assembly process and line of the optical pickup device described above can be simplified.
Preferably, the optical pickup device according to the present invention further includes a supporting member, and the case and the supporting member are connected by a supporter, and the case is movably semifixed to the supporting member.
According to this configuration, all the optical components of the optical pickup device are integrally movable. Therefore, when the focusing/tracking servo is carried out with respect to an optical disk, no optical shift is caused and thus reliable recording and reproducing characteristics can be obtained.
In the semiconductor laser device according to the present invention, preferably, the first and second semiconductor laser elements are integrated in one chip.
According to this configuration, a plurality of semiconductor laser elements are integrated in one chip, so that a semiconductor laser device with a reduced number of components can be obtained. This enables the size of the optical pickup device to be reduced.
In addition, in the semiconductor laser device according to the present invention, it is preferable that the optical element is placed on the receiving/emitting optics integrated substrate.
According to this configuration, the optical element is placed on the receiving/emitting optics integrated substrate, so that a semiconductor laser device with a protected receiving/emitting optics integrated substrate can be obtained. Consequently, the reliability of the optical pickup device can be improved.